2O FRANK R. LILLIE. 



It is thus impossible to establish any relationship between cross 

 agglutination and cross fertilization ; i.e., to predict from the 

 cross-agglutination of franciscanus sperm by purpuratus egg- 

 water what the success of the cross-fertilization of these eggs 

 might be. This result is to be expected from the conclusion that 

 the apparent cross agglutination is caused by a substance distinct 

 from the purpuratus fertilizin, that is, by a substance not directly 

 concerned in fertilization. 



GENERAL. 



The outstanding result of the investigation is that the reaction 

 of the egg to the spermatozoon and the reaction of the sperma- 

 tozoa, by agglutination, to egg secretions are both highly specific. 

 Fertilization and agglutination run in the same direction, and this 

 gives strong new additional evidence that there is a specific con- 

 nection between fertilization and the capacity for agglutination 

 of the spermatozoa. It is in fact hardly conceivable that such a 

 reciprocal specificity between egg and spermatozoon should be 

 without significance. 



Let me now deal with the apparent difficulty that agglutina- 

 tion (the reaction of the sperm to egg-secretions) appears to be 

 more specific than fertilization (the reaction of the egg to the 

 spermatozoon). As I have already pointed out in the present 

 paper, the agglutination reaction will detect only such changes in 

 the individual spermatozoa as will cause them to adhere to one 

 another; any change below this threshold will fail to be dis- 

 tinguished. On the other hand, the fertilization reaction is to be 

 detected in the individual egg. A higher degree of detectible 

 specificity may therefore be expected for the agglutination reac- 

 tion than for the fertilization reaction. 



Secondly, the adhesion of spermatozoa to one another is no 

 part of the process of fertilization ; indeed, such adhesion could 

 not occur in the sperm concentrations ordinarily used in fertiliza- 

 tion, or occurring in nature, owing to the wide dispersion of the 

 spermatozoa. It is the change in the individual spermatozoon 

 and the postulated reciprocal change in the fertilizin that is 



